(221g) Colloidal Particles and Planar Substrates with Stimulus-Responsive Surfaces of Tunable Roughness

Surface roughness is known to influence the wetting properties of solid substrates, and the wetting properties of colloidal particles determine their ability to stabilize emulsions. Here we report the preparation of substrates and particles with tunable surface roughness via adsorption of nanoparticles synthesized from polymers with pH-switchable water solubility. The surface roughness caused by the adsorbed nanoparticles can be reduced to various extents via pH-triggered (partial) particle dissolution or by particle fusion upon exposure to a plasticizing co-solvent and slightly elevated temperature. The achievable degrees of roughness are studied by scanning electron microscopy and atomic force microscopy, and the charging state of the surfaces in contact with aqueous solutions is monitored electrokinetically. Contact angles between substrates of systematically varied roughness and air-water or oil-water interfaces were measured to characterize the influence of roughness on wetting, and colloid particles with similarly varied roughness were tested as stabilizers for surfactant-free emulsions. Our results illustrate the importance and versatility of surface roughness in the design of interfacial properties.